The present invention relates to a process for the preparation of herbicidal 1-alkyl-4-(2-chloro-3-alkoxy-4-alkylsulfonylbenzoyl)-5-hydroxypyrazole compounds and of certain 1-halo-2-chloro-3-alkoxy-4-alkylsulfonylbenzene compounds that are useful intermediates in the manufacture of these herbicidal compounds. More particularly, the present invention concerns the preparation of 2-chloro-3-alkoxy-4-alkylsulfonylbenzoic acids and esters by carbonylation of the corresponding 1-chloro compounds.
A number of 1-alkyl-4-(2-chloro-3-alkoxy-4-alkylsulfonylbenzoyl)-5-hydroxypyrazole compounds were disclosed in U.S. Pat. RE-34,779 and were reported to possess excellent herbicidal properties. These compounds were prepared by the reaction of a 1-alkyl-5-hydroxypyrazole compound with a 2-chloro-3-alkoxy-4-alkylsulfonylbenzoic acid compound. The preparation of the 2-chloro-3-alkoxy-4-alkylsulfonylbenzoic acid compounds used as starting materials was carried out by alkylation of 2-chloro-3-hydroxy-4-alkylsulfonylbenzoic acid compounds. The 2-chloro-3-hydroxy-4-alkylsulfonylbenzoic acid compounds required for this procedure can be obtained by hydrolysis of a 2,3-dichloro-4-alkylsulfonylbenzoic acid compound. This reaction and the alkylation process were disclosed in U.S. Pat. No. 4,898,973. The preparation of 1-alkyl-4-(2-chloro-3-alkoxy-4-alkylsulfonylbenzoyl)-5-hydroxypyrazole compounds by this route requires many reaction steps and produces large quantities of unusable by-products and waste. More direct and economical methods of production are highly desirable.